A. Technical Field
The present invention relates to a cement dispersant, its production process, and a cement composition using the cement dispersant. More specifically, the invention relates to: a cement dispersant which is excellent in initial dispersibility and further in flow retainability of cement; a process for producing this cement dispersant; and a cement composition using this cement dispersant.
B. Background Art
Cement is often used in civil engineering and building sites. Cement paste (obtained by adding water to cement), mortar (obtained by mixing the cement paste with sand as fine aggregate), and concrete (obtained by further mixing the mortar with ballast as coarse aggregate) are used for many purposes such as structural materials, civil engineering, and fire walls, and their quantities are also large. As to these cement paste, mortar, and concrete, their strength is produced via cohesion and hardening by hydration reaction between cement and water, so the workability becomes worse with the passage of time after the addition of water. Particularly, since early deterioration of concrete structures became social problems in 1981, it has been strongly required to improve execution and durability of the concrete structures by decreasing the unit quantity of water in concrete. Thus, technological innovation is carried out to cement additives which have much influence on the quality and the performance of cement compositions.
Various cement additives, such as naphthalenic, aminosulfonic, and polycarboxylic ones, have hitherto been developed, and those which are known as excellent polycarboxylic high-performance water-reducing agents are as follows: a copolymer obtained by copolymerizing such as a polyalkylene glycol mono(meth)acrylic acid esteric monomer and a (meth)acrylic monomer in a specific ratio as disclosed in JP-B-018338/1984; and a copolymer obtained by copolymerizing such as an unsaturated polyalkylene glycol etheric monomer and a maleic monomer in a specific ratio as disclosed in JP-A-236858/1998.
These polycarboxylic high-performance AE water-reducing agents have high water reducibility and slump retainability, but these performances are not yet sufficiently satisfiable, therefore more improvement of these performances is demanded.
Generally, performances of cement dispersants correlate with molecular weights of polymers as used. In the case where the molecular weight is small, the dispersibility, particularly, initial dispersibility, is excellent, but there are also problems in that the quantity of air becomes excessive. On the other hand, in the case where the molecular weight is large, the flow retainability of cement is excellent, but there are also problems in that addition of a large quantity of cement dispersant becomes necessary for obtaining the same flow value.